I love the build I am riding now: Hadley hub, 32 db spokes, WTB Frequency Team i25 rim. If I had to rebuild, I would be fine with a Hope or Bitex hub to save on the cost. I like the DT hubs but you have to pay quite a bit extra for the higher POE bits and, riding singlespeed, I feel higher POE is important.

A DT350 hub with 36 or 54t ratchet upgrade, Sapim Laser spokes and Polyax nipples from Dans Comp.
I would choose a 35mm inner width rim and run Bontrager XR Team tires in 2.35 or 2.4. They have a more rounded profile to work better on wider rims at lower pressures. A XR4 2.5 or 6 is coming soon. https://www.danscomp.com/Sapim/bmx/